hi ya there Mike
First may I ask a question? Do you own/possess the JJC mixer unit? If so, there are a couple of things that you maybe should consider - before opting to using this mixer.
The first one to think about is that JJC Company is now no longer in existence and having repairs done to their units is becoming increasingly difficult. In fact, I am unsure whether there is anyone who has had any of the JJC units repairs successfully - of course I may be wrong there.
The second thing to consider is, I am unsure as to whether the JJC mixer is indeed compatible with any other manufacturers electrical components. These are just a couple of things to think of a first; right....
so....I presume we are talking about your Whaleback build and power units; so therefore the power units will be either 700s or 800s motors. These are large thirsty motors, when I say thirsty, I mean they draw heavy amperage.
Now there are severally commercially available speed controllers on the market today; which are capable of handling these motors - it depends upon your preference. Now I know the above posting mentions ACTions twin speed controller and mixer combined; I very much doubt whether this is capable of handling the power requirements of the 800s or the 700s to be precise - however, they do produce a mixer on its own - which is compatible with about 95% of commercially available speed controllers. This particular mixer does have the facility of taking 3 x speed controllers. The 2 outer speed controllers which it controls are mixed with your rudder. The centre speed control is not affected by the mixing of the 2 - it is only affected by the position of your throttle stick. This is what you require:
It is a very straightforward and easy set up as long as you take your time, and, read the instructions.
I have used many of these mixers in my models, with a great success and no complaints. Having said that though, I have used these mixers on an ACTion speed controllers, Electronize speed controllers, MAPLINS' - 'old' speed controllers
which are unobtainable now and also home-made speed controllers.
I would suggest Electronize 30 amp speed controllers to be used; but, they are very expensive - talking about 120 pounds sterling for 3 maybe more. The time has come the walrus said....for Wom and ACTion to produce a 30 amp speed controller HINT HINT....

Hope this is of some help,
aye
john e
bluebird